This invention relates to a process for removing ozone from an ozone-containing gas which comprises treating the gas with a calcined molding product composed of activated carbon-zeolite mixture.
Ozone is a gas which has a strong oxidative action. So, ozone is widely used in oxidizing step for removing noxious material and smell component, and in decoloring. Ozone is also used in tertiary treatment of wastes. However, since ozone is noxious to a living body, it is necessary to make ozone-containing waste gas innoxious after use of ozone. When an ozone-containing waste gas is directly discharged into the atmosphere, oxidant generated through photochemical reaction acts to cause secondary environmental pollution. So, it is necessary to remove ozone from an ozone-containing waste gas from the view point of preventation of environmental pollution, until the ozone content of the gas is below the upper limit by government regulations.
Numerous attempts have been made to decompose ozone present in an ozone-containing waste gas. The following prior art processes have been carried out:
(a) a process for decomposing the ozone through heat or light, PA1 (c) a process for decomposing the ozone using a catalyst.
(b) a process for decomposing the ozone through chemical reaction using a reductant, such as potassium iodide, and
The conventional process for decomposing ozone uses activated carbon as a catalyst. Processes for decomposing ozone using a metal compound-carrying activated carbon, and using graphite or carbon black in place of activated carbon have been attempted. Also combinations of (c) and (a), or (c) and (b) of the above processes have been attempted.
In the process for decomposing ozone using a catalyst, the following chemical reaction occur: EQU C+O.sub.3 .fwdarw.CO+O.sub.2 (i) EQU C+O.sub.3 .fwdarw.CO.sub.2 +1/2O.sub.2 (ii)
In the prior process for decomposing ozone using activated carbon, activated carbon is converted to carbon monoxide and carbon dioxide. When the above reactions (i) and (ii) are carried out, the temperature of the catalyst bed is raised through heat of the reaction. This is undesirable. For example, when waste gas having a high ozone content is treated with only an activated carbon bed, the above chemical reactions proceed vigorously, whereby the temperature of the catalyst bed is rapidly raised. Therefore, the catalyst bed catches fire, and in the worst case, explosion of the bed may occur.
When activated carbon is used for decomposing ozone, the activated carbon is formed into pellet shape, tablet shape or particulate shape, and the molded activated carbon is charged into a column. However, in this case, according as the use of the molded activated carbon is continued, the activated carbon is gradually consumed whereby the mass becomes smaller one. Therefore, it is made difficult to pass an ozone-containing gas through the activated carbon bed.